1. Field of the Invention
The present invention relates to a covert, expendable infra-red (IR) radiating means and in particular to a covert countermeasure or decoy flare capable of generating an IR interference cloud to divert an incoming missile equipped with an IR seeker system away from its intended target or to create a covert IR screen.
2. Discussion of Prior Art
Known IR decoy flares conventionally comprise pyrotechnic compositions bound together with an organic binder and pressed to form pellets. When an incoming missile is detected a pellet is ignited and launched from the target. The pellet burns over its surface to produce an intense infra-red source which can lure the infra-red seeker system of the missile away from the target.
However, advances in missile seeker systems and the development of ‘intelligent’ missile systems have led to seeker systems which are designed to recognise the typical characteristics of a decoy flare and ignore it. Some advanced seeker systems are programmed with a characteristic infra-red signature of the intended target, the exhaust plume of a jet aircraft for example, and will ignore the almost point like radiating source of a conventional flare.
There has therefore become a need for a countermeasure which radiates over a large area, either to appear more like the intended target to the missile system or to act as a screen, especially for larger or slower moving targets.
One known decoy flare which is capable of generating a large cloud emitting in the infra-red range is described in the U.S. Pat. No. 4,624,186. This flare comprises a casing containing combustible flakes and an ignition expediting material. These combustible flakes comprise a thin base material, such as paper or metal foil, on to which is pressed a phosphorus containing incendiary paste. In use, the flare is launched into the air and the ignition expediting material creates a fireball which passes through the combustible flakes, igniting the incendiary paste which burns to emit IR radiation and spreading the flakes which float slowly downward creating the interference cloud.
One problem with this type of flare is that phosphorus has a characteristic IR emission spectrum which some ‘intelligent’ seeker systems can be programmed to ignore. Also, these types of flares are quite expensive. Further this type of flare also radiates in the visible and ultra-violet (UV) regions and produces a large, visible smoke cloud. This has the disadvantage of revealing that a countermeasure has been deployed which can indicate that a certain threat has been detected.
Furthermore, some ‘intelligent’ seeker systems use other radiation, for example UV emission, when deciding to ignore some IR sources and are therefore not deflected by flares emitting significant amounts of radiation in the visible or UV regions. Also, some missile systems, for example ones often employed in ground based anti-aircraft batteries, require human operators to make an initial target acquisition for a particular missile before the IR seeker system of that missile guides it to its acquired target. This target acquisition is done visually and hence, particularly at night, illumination of the target by the visible emission from the decoy is undesirable.
One known type of covert flare uses Activated Metal Disks (AMDs). These are disks of metals made pyrophoric by a process described in U.S. Pat. No. 4,895,609. The disks are held in a store which, on ejection from the target, ruptures to dispense the disks. As the disks are pyrophoric they ignite on contact with the air and burn to act as a decoy.
However this type of flare is expensive to produce and, due to the pyrophoric nature of the disks, has a relatively large delay before becoming effective as the disks have to be ejected and dispensed before ignition can occur. For some applications, e.g. for fast moving vehicle decoys, the narrow field of view of some modern seeker systems means that the disks can be outside the missiles effective vision by the time combustion is fully underway and will not therefore be effective as a decoy. Also, the mass of a flare of this type can be significantly greater than standard IR flares.